TL:DR/ - Is it possible this is just a bad downstream B1/S2 sensor or does this look more like the cat starting to go?
Background:
So, I have a 2012 Grand Caravan with the 3.6 and 230K miles. I replaced the leaking oil cooler about 10K miles ago and inadvertently let some oil get down into the rear intake ports. Next day I got a P0420 code for the right Cat, which I assumed was because of the oil. I reset the mil code and ran the van pretty hard for a few days to try to burn off any oil in the cat. Van ran fine and code never came back until now, 10K miles and four months later.
Even with the new P0420 code, the van still runs great, no misfires, fuel trims are good, and no loss of power. Live data on my scan tool shows normal B1S2 voltage at low idle but some random dips at higher idle and when driving. At normal idle, the downstream voltage is pretty steady around .72 or so.
Is the cat starting to go or could this be a bad downstream O2 sensor?
Thanks.
Brian
Background:
So, I have a 2012 Grand Caravan with the 3.6 and 230K miles. I replaced the leaking oil cooler about 10K miles ago and inadvertently let some oil get down into the rear intake ports. Next day I got a P0420 code for the right Cat, which I assumed was because of the oil. I reset the mil code and ran the van pretty hard for a few days to try to burn off any oil in the cat. Van ran fine and code never came back until now, 10K miles and four months later.
Even with the new P0420 code, the van still runs great, no misfires, fuel trims are good, and no loss of power. Live data on my scan tool shows normal B1S2 voltage at low idle but some random dips at higher idle and when driving. At normal idle, the downstream voltage is pretty steady around .72 or so.
Is the cat starting to go or could this be a bad downstream O2 sensor?
Thanks.
Brian
Images (Click to enlarge)
Jun 2, 2026 at 5:40 AM
